1. Biological Base Flashcards
Hierarchy of size
nucleus - chromosomes - DNA - genes
Chromosomes
Thread-like structures
Every cell has 46 chromosomes, 23 pairs
23 pairs - one half of the pair from each parent
Contain DNA
DNA
Complex molecule
Double helix shape
Chain of nucleotides
Contains genetic information
DNA bases
AT GC - have to be paired this way
Made of nitrogen
Nucleotides
phosphate + sugar + base = nucleotide
Genes
- Short sections of DNA
- Units of hereditary information
- Help cells reproduce & assemble proteins (building blocks of cells)
- Each have specific locations
Mitosis
The process by which the nucleus of the cell duplicates & divides to create two genetically identical daughter cells
Mitosis process
- Chromosomes duplicate (becoming the X)
- Move to opposite ends of the nucleus
- Nucleus divides
see diagram
Meiosis
The process by which germ cells divide, creating two genetically unique gametes with half the chromosomes of the original cell (23 from 46)
Germ cell
Cells that produce gametes
Gametes
Sperm and ova cells
Meiosis Process
- 46 chromosomes are duplicated
- Crossing-over
- Duplicated chromosomes divided into 2 cells (each with 46 chromosomes)
- New cells divide again
Result: 4 cells with 23 single/unpaired chromosomes
Either sperm or ova
see diagram
Crossing-over
Genetic material is exchanged between pairs of chromosomes
1. Duplicated chromosomes break at one of more points and swap pieces with adjacent pairs
Hereditary uniqueness/independent assortment
Children receive 23 unpaired chromosomes from each parent, combining to given them a unique combination of 46
- There are trillions of possible combinations & distributions
- Down to chance which unpaired chromosomes go into what cells
- Includes the newly merged chromosomes from crossing over
Monozygotic twins
One cell split into 2
Dizygotic twins
Two cells released at the same time
Female sex chromosome
XX
Ova only have X chromosomes
Male sex chromosome
XY
Sperm have either X or Y chromosomes
First trimester
Zygote
Embryo
Fetus
Zygote - week 1
Singular celled zygote divides into a blastocyst
Zygote - week 2
Blastocyst implants into uterine wall
Structures begin to form:
- Amnion
- Chorion
- Yolk sac
- Placenta
- Umbilical cord
Nourish & protect the cell
Embryo - 3-4 weeks
- Brain
- Spinal cord
- Heart
Rudimentary structures (to become)
- Eyes
- Ears
- Nose
- Mouth
- Limbs
1/4 inches
Embryo - 5-8 weeks
External structures form
- Eyes
- Ears
- Limbs
Organogenesis - internal organs form
Abilities
- Produces its own blood
- Can move
Fetus - 9-12 weeks
First trimester
Rapid growth & interconnection of organ systems lead to
- Body & limb movements
- Swallowing
- Urination
- Digestion
External genitalia form
Fetus - 13-24 weeks
Second trimester
- Rapid growth
- Movements felt by mother
- Heartbeat can be heard
- Covered by vernix
- Reacts to bright lights & sounds
Fetus - 25-28 weeks
- Growth continues
- Organ systems mature
- Age of viability reached
- Predictable sleep cycles & motor activity
- Fat layer under skin develops
- Less activity, more sleep